Atomizing aluminum



Dec. 27, 1955 F. HERSHEY 2,723,107

ATOMIZING ALUMINUM Filed Sept. 18, 1953 2 Sheets-Sheet 1 I N V EN TOR. 60/00/7 E Hans/16y ATOMIZING ALUMINUM Gordon F. Hershey, Midland, Mich., assignor to The Dow Chemical Company, Midland, Mich., a corporation of Delaware Application September 18, 1953, Serial No. 380,928 4 Claims. (Cl. 1847.2)

The invention relates to methods of atomizing metal. It more particularly concerns an improved method of atomizing aluminum and the aluminum-base alloys.

The principal object of the invention is to provide a method of atomizing aluminum and the aluminum alloys in which these metals are converted from the liquid state into a mass of fine smooth spherical particles each having a size which differs but little from their average size. Other objects and advantages will appear as the description of the invention proceeds.

The invention is predicated upon the discovery that by letting fall the molten metal in a thin stream onto a rapidly revolving disc'of carbon or graphite in a cool neutral gas atmosphere, the disc being maintained at a temperature above the melting point of the molten metal, the metal is flung off the disc in very fine and quite uniformly sized spherical droplets which solidify in smoothuncontaminated spheres. The invention then consists of the improved atomizing method herein fully described and particularly pointed out in the claims.

In carrying out the invention, the aluminum or aluminum alloy to be atomized is melted and brought to a temperature in the range of 675 to 800 C. or preferably between about 685 and 725 C. The molten metal is then allowed to fall in a thin solid stream (e. g. /8 to M4 inch in diameter), a distance of between about 1 /2 and 14 inches, or preferably about 6 to 8 inches onto a spinning disc of carbon or graphite the axis of rotation being vertical. The length of the fall is not great enough to cause the falling stream to separate into drops or slugs as this interferes with satisfactory atomizing. The point of impingement of the molten metal on the disc is at or near its center. i

A concave disc having a spherically concave atomizing surface is preferred to a flat or other surface shape. Discs having a diameter of 2 to 6 inches may be used. A preferred diameter is 3% inches with running speeds of 5000 to 15,000 R. P. M. or more depending upon the diameter and strength of the carbon or graphite used. To prevent bursting of the disc at high rotational speeds, it may be reinforced with steel asby encasing the periphery with a steel band or by placing the disc in a recess in a steel cup which is revolved.

The space in which the disc operates is charged with a neutral gas such as natural gas or with one or more of the principal hydrocarbon constituents thereof, e. g. methane, ethane, propane, butane, preferably at room temperature, although temperatures up to about 240 C. may be used. The so-called inert gases may be used, c. g. helium, argon, and are preferable for use at the higher of the useful operating temperatures which may be as much as 100 Centigrade degrees below the melting point of the metal. The temperature of the disc is important. It is brought up to and maintained at Working temperature by themolten metal to be atomized. Maintenance of the disc at proper working temperature is facilitated by at least partially insulating it against heat loss as by a backing of thermal insulation. With the Working surface of the nited States Patent-O disc at the proper working temperature (above the M. P. of the metal), the disc remains smooth and splashing is virtually eliminated with the consequent elimination of the formation of olf size and non-spherical particles. The sieve analysis of the atomized product remains substantially constant duringoperation. The amount of extremely line or dust-like particles formed, if any, is negligible. Instead, the molten metal is atomized into a mass of spherical particles conforming to a relatively narrow range of desirableparticle sizes.

The invention may be further explained and illustrated by reference to the accompanying drawing showing an apparatus with which the method may be practiced.

In the said drawing wherein like numerals designate like parts:

Fig. 1 is a diagrammatic view of the atomizing plant showing the elements thereof and their relationship;

Fig. 2 is a detailed view largely in section of a portion oftlie apparatus of Fig. 1; g

' Fig. 3 is an enlarged sectional view on the line 3-3 of Fig. 2.

Referring to the drawing and more particularly Fig. 1, there is shown an atomizing tank 1 in which atomization takes place. The tank has a conical bottom 2 having an outlet 3 which is connected by pipe line 4 to a settling tank 5. The settling tank 5 has an outlet 6 at the bottom the opening through which is subject to control by a valve 7. The settling tank is connected by a pipe 8 to the cyclone separator 9. The separator is provided with a bottom outlet 10 controlled by a valve 11. The top outlet 12 of the separator 9 is connected by a pipe 13 to a gas holder 14 which holds a supply of inert gas which may be introduced through the inlet pipe 15 connected to a source not shown. Inert gas is withdrawn from the gas holder 14 through pipe 16 by means of the gas compressor 17. Thegas compressed by the compressor 17 is delivered through pipe 18 to the cooler 19 in which the compressed gas is cooled. The cooled compressed gas passes from the cooler through pipe 20 to the turbine 21, shown in Fig. 2 in tank 1.

Referring more particularly to Fig. 2, turbine 21 is supported on legs 22 the lower ends of which (not shown) are secured to the inside of tank 1. The turbine 21 drives the'vertical spindle 23 to the upper end of which is welded chuck 24 shown in detail in Fig. 3. As shown, the outer end of the chuck is provided with a recess defined by the flat bottom 25 and cylindrical side a wall 26. Fitted into the recess is the atomizing disc 27 -II- graphite is mixed with a J known in the art of The particular form of the carappear to be critical provided it strength. For example, there graphite wherein finely-divided resinous binder, e. g. phenol formaldehyde resin, and molded under pressure. Hard carbon, such as petroleum coke, may be formed similarly into a suitable disc. If desired, the binder, if used, may be carbonized or even graphitized by heating as is wellmaking molded carbon and graphite articles. Thus, in the claims, the term carbon or graphite is used to mean any of'the commonly available forms of rigid massive carbon or graphite having adequate structural strength for the purpose. In fitting the disc 27 into the recess of the chuck 24, the lower end 28 of the disc is separated from the bottom 25 of the chuck by a layer 29 of thermal insulation, such as for example asbestos paper /8 inch thick. The upper face 30 of the disc is concave and conforms in shape to the surface of a sphere. The rim 31 of the disc 27 extends above the rim 32 of the recess.

As shown in Fig. 2, the top 33 of tank 1 has a centraldisposed concave portion 34 on which is mounted the furnace setting, indicated generally by numeral 35. This of carbon or graphite.

bon of the disc does not has adequate mechanical may be used resin bonded is comprised of a relatively smaller diameter lower portion 36 and an upper portion 37 having a larger diameter so as to accommodate a melting pot 38. Attached to the bottom of the melting pot and forming an outlet therefor is the tubular spigot 39 having an outlet 40 of smaller diameter than the bore 41 of the spigot. Between the outlet 40 and the bore 41 is a shoulder 42 which forms a seat for a valve 43. As shown, the valve 43 is formed as a shoulder on the lower end of the push rod 44 which enters the bore 41 of the spigot 39. The push rod also carries a smaller diameter portion 4-5 as a prod capable of being pushed through the outlet 40 to clean it as the valve 43 engages the shoulder 42 in closing the outlet 40.

The spigot has an external taper 46, the taper being designed to seat in the internally tapered nipple 47, as shown, the bottom of which is joined to the concave portion 34 of the tank 1 around the central opening 43. The outlet 40 is directly above the center of the disc 27, a distance of about 1 /2 to 14 inches. The furnace setting 35 is provided with openings 49 and 50 in the lower and upper portions, respectively, through which the flame of heating burner (not shown) is projected to heat the tapered nipple 47, spigot 39, and melting pot 33 to a suitable operating temperature. Telescope 52 is provided for viewing the atomizing disc.

in operation, when starting up, the opening 40 is closed by lowering the push rod 44 so as to seat the valve 43 on shoulder 42 and a charge of the metal to be atomized is introduced into the melting pct 38. The operating depth or" metal in the pot is from about 1 inch to 30 inches in the pot. The pot is maintained sutficiently hot to maintain the charge at about 675 to 800 C. The compressor 17 is started up and inert gas is thereby withdrawn from the gas holder and compressed. The compressed gas is discharged from the compressor through pipe 13 into the cooler 19 which removes more or less of the heat of compression. The so-cooled compressed gas is delivered by pipe 20 to the turbine 21, thereby spinning the atomizing disc 27. The exhaust from the turbine enters the tank 1 by way of the turbine exhaust pipe 53 and maintains in the tank an inert gas atmosphere. When the disc 27 reaches a suitable speed of rotation, e. g. 10,000 R. P. M., the push rod 44 is raised enough to allow the molten metal from pot 38 to fall in a thin stream 54 through the opening 40 onto the con-- cave surface 30 of the disc 27 while it spins. After a time, the disc 27 acquires a suitable operating temperature, viz. a temperature above the melting point of the metal to be atomized. The molten metal wets the heated disc surface but does not attack it. The molten metal is flung oil the disc when hot enough in tiny uniformly sized spherical drops which solidify into spherical particles in the inert gas atmosphere of the tank 1. The atomized particles thus produced fall onto the conical bottom 2 and are carried by the inert gas, exhausting from the turbine, through the outlet 3 into pipe 4 and thence into the settling tank 5. Most of the particles settle out of the inert gas in the tank and may be withdrawn from time to time through the outlet 6 by opening valve 7. The relatively small amount of fines which do not settle out of the o inert gas in tank 5 are carried into the cyclone separator 9 by the inert gas which flows from tank 5 into the cyclone through pipe 8. The inert gas separated from the fines in the cyclone separator is discharged through pipe 13 into the gas holder 14 for recirculation through the system as described. From time to time, the fines may be withdrawn from the cyclone separator through outlet 10 by opening valve 11.

As the operation proceeds, the tank 1 heats up to an extent which depends upon the temperature of the molten metal, rate of input of metal, the heat dissipating characteristics of the tank, and the temperature of the incoming inert gas as well as the cooling effect of the expansion of the inert gas in driving the turbine 21. In general, it is desirable to keep the inert gas temperature in the atomizing zone, i. e. the area adjacent to the spinning disc 27, below the temperature capable of being withstood by the gas used without decomposition. Temperatures in the range of to 240 C. are generally satisfactory for hydrocarbon gases.

Among the advantages of the invention are that the atomized particles are spherical and free flowing. The particles fall into a narrow range of sizes so that little, if any, screening is necessary to obtain a uniform product.

As a consequence, little, if any scrap is formed necessitating remelting and reworking. The size of the particles is controllable by varying the rotational speed of the disc. The higher the disc speed the smaller the particles are.

I claim:

1. The method of atomizing aluminum and aluminum alloys which comprises maintaining a body of the metal in the molten state at a temperature between 675 and 800 C. letting the molten metal fall a distance of 1 /2 to 14 inches in a thin solid stream onto a rapidly revolving disc having a surface comprising carbon, the surface of the said disc having a temperature above the melting point of the metal, while maintaining about the disc a neutral atmosphere having a temperature below the melting point of the metal.

2. The method according to claim 1 in which the disc comprises graphite.

3. The method according to claim 1 in which the at mosphere comprises an inert gas having a temperature .lower than 100 centigrade degrees below the melting point of the metal.

4. The method according to claim 1 in which the atmosphere comprises a hydrocarbon gas at a temperature below 240 C.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Ser. No. 268,381, Kaufmann (A. P. C.), published July 13, 1943 (abandoned). 

1. THE METHOD OF ATOMIZING ALUMINUM AND ALUMINUM ALLOYS WHICH COMPRISES MAINTAINING A BODY OF THE METAL IN THE MOLTEN STATE AT A TEMPERATURE BETWEEN 675* AND 800* C. LETTING THE MOLTEN METAL FALL A DISTANCE OF 1 1/2 TO 14 INCHES IN A THIN SOLID STREAM ONTO A RAPIDLY REVOLVING DISC HAVING A SURFACE COMPRISING CARBON, THE SURFACE OF THE SAID DISC HAVING A TEMPERATURE ABOVE THE MELTING POINT OF THE METAL, WHILE MAINTAINING ABOUT THE DISC A NEUTRAL ATMOSPHERE HAING A TEMPERATURE BELOW THE METALING POINT OF THE METAL. 